As an autofocus detection (autofocus: AF) method for image capture apparatus, a TTL phase difference detection method used by single-lens reflex cameras is conventionally known. The TTL phase difference detection method is a method that divides part of a captured light beam in two, detects the direction and amount of shift between these two images, and thereby calculates the direction and amount of movement of the focus lens required to achieve focus at a desired focal plane (a plane conjugate to the imaging plane). In order to divide the light beam that has passed through the exit pupil of the imaging lens in two and obtain signals corresponding to the respective light beams, usually, optical path dividing means, such as a quick return mirror or a half mirror, is provided in the imaging optical path, and a focus detecting optical system and an AF sensor are provided in the rear of the optical path dividing means. In this specification, autofocus detection by the phase difference detection method that uses an AF sensor provided separate from the image sensor as described above is referred to as the “sensor-separated phase difference detection method”. The sensor-separated phase difference detection method has the advantage that the focusing operation can be performed in a short time because it can directly calculate the driving direction and driving amount of the focus lens required for focusing. However, this method also has the disadvantage that because it requires a separate sensor and optical components, it is necessary to provide a relatively large space within the image capture apparatus.
On the other hand, there is another autofocus detection method in which a pupil division function that can detect the amounts of image shifts in the horizontal and vertical directions is assigned to some of the pixels of the image sensor to enable so-called phase difference AF. In this specification, this method is referred to as the “sensor-integrated phase difference detection method”. The sensor-integrated focus detection method, the details of which will be described later, has the problem in that the exit pupil is vignetted depending on the aperture of the imaging lens, as a result of which accurate focus detection is not possible. To address this, Japanese Patent Laid-Open No. 2004-191629 discloses a technique that enables more precise focus detection by performing shading correction on image signals that are used for correlation calculation of the phase difference AF by using imaging lens exit window information and focus detection region information of the lens.
However, because such a configuration requires shading data based on the imaging lens exit window information and the focus detection region information, a large capacity storage region is necessary when actual measured shading data is stored as adjustment values. In addition, even when shading correction is performed by using values calculated by simulation or the like, there is a problem in that variation between lenses due to manufacturing error cannot be absorbed.